This invention relates to an oilfield cleaning apparatus and a method for cleaning the inner wall of an oilfield tubular. Such apparatus can be used for cleaning casing or pipeline tubulars in the petroleum industry, either downhole or when used on the surface or subsea for the transmission of oil or gas.
When running casing into a borehole in the construction of oil and gas wells, cement is commonly used to seal the casing into the hole and to seal between casings. This cement leaves scale residues in areas on the casing where it is not required, and cleaning tools must be used to remove such residues.
Furthermore oil or gas is prone to produce scale deposits, such as barium sulphate and calcium carbonate, on the inner walls of production tubing, and such scale deposits must also be removed using cleaning tools from time to time to prevent restriction of production rates.
Additionally oil produced from oil wells may in some cases carry high levels of wax which, as the oil cools, itself produces deposits along production flow lines. These deposits are also a form of scale which must be removed by use of cleaning tools if the oil transmission rate is to be maintained. In some cases, water produced with the oil carries with it minerals, such as calcium and barium, which can also be deposited in layers on the inner walls of production flow lines, together with the wax, to create laminated scales which can be very difficult to remove.
In all the above cases, it is necessary to use cleaning tools and/or chemical solvents to remove the unwanted deposits. However the mechanisms and cleaning tools used to remove the various scales encountered in the petroleum industry have not changed significantly for many years. In the case of cement scales, the mechanical scrapers or fixed brushes employed have to be moved up and down the tubular to produce the required cleaning action. An example of a prior reference disclosing such a cleaning tool is U.S. Pat. No. 4,896,720. Furthermore milling has been employed to remove the harder scales, such as barium sulphate and calcium carbonate. In addition chemical solvents have been used in isolation and together with mechanical removal systems, with varying degrees of success. In production pipelines, cleaning pigs are usually used in association with solvents, but this is an expensive exercise which needs to be repeated many times for effective cleaning.
It is an object of the invention to provide an improved technique for cleaning oilfield tubulars, such as pipe and casing sections, in such applications.
According to the present invention there is provided oilfield cleaning apparatus for cleaning the inner wall of an oilfield tubular, the apparatus comprising a body to be introduced into the tubular, the body being provided with at least one cleaning element, and drive means acting to oscillate the cleaning element in contact with the inner wall of the tubular to scrape the inner wall with the cleaning element.
Such apparatus obviates the shortcomings of the prior art in that it provides an active cleaning action, which can be rotary, motor or turbine driven, utilising one or more oscillating cleaning elements. The cleaning elements can be grouped in modules on a common drive shaft, and the drive shaft can be used to drive an impeller which guides heavy debris not circulated out of the tubular to be drawn into a catcher element.
The invention also provides a method of cleaning an inner wall of an oilfield tubular, the method comprising introducing into the tubular a body provided with at least one cleaning element so that the cleaning element contacts the inner wall of the tubular, and operating a drive to oscillate the cleaning element to scrape the inner wall with the cleaning element.